Air-supported flexible fabric structures include army shelters, collapsible fuel and water storage tanks, communication radomes and radar radomes for antenna protection, hangars, shelters, sporting complex “domes” and other structures. Such fabric structures provide for a controlled environment and serve as protection from thermal distortions, sunlight, rain, and other elements. In other examples, engineered inflatables using fabric include airships, aerostats, blimps, air beams and air floats, air bags, and impact absorbers. Architectural fabrics can also be found in sports complexes, transportation complexes, amphitheaters, and outdoor pavilion covers. Industrial fabric applications can be found in odor containment covers for municipal and industrial wastewater treatment tanks.
Currently, high strength, structural fabric seaming technology utilizes heat weldable, thermoplastic, “overlap” or “butt-joint” seams to join together various fabric sections that make up the fabric structure. In fact, all known high strength fabric structures use “overlap” or “butt-joint” techniques.
A disadvantage of current fabric structures and seam configurations is that they produce undesirable thickness discontinuities in the resulting structure. Among other things, these thickness discontinuities cause localized stress concentrations which increase strength demands on the overall structure. And, for radar applications, such as the use of fabric in radomes, radio frequency (RF) transmission losses result from the thickness discontinuities produced by “overlap” or “butt-joint” seams. RF waves travelling through thicker areas of the radome created by overlapping or butt-joint seams travel at slower speeds, are reflected or scattered, and thus cause undesirable radio frequency losses and a reduction in RF performance. Consequently, more power is required to compensate for RF losses, at great expense. A reduction in performance of 15-20% produces a loss on the order of 0.10 dB, and such a loss may translate into a seven figure cost increase in the radar system protected by the radome.